Question

The effect of a given sound lasts on the human ear for about 0.1 sec . Use this fact along with a knowledge of the speed of sound (~_300ms-1 )to estimate the minimum distance of the reflecting object for getting a clear and distinct echo

Answer 1

As given, speed of sound is 300ms-1
For echo, the sound has to first travel from the source to the reflecting body and again back in 0.1 second.
Let the distance between the source and reflecting object be X.
Therefore sound has to travel distance of 2X in 0.1 second.
Thus,
300*0.1 will gove the total distance to be travelled, which gives 30 metres.
Thus
30 m is to be travelled.
Thus 2X = 30.
Therefore
X=30/2=15.
Distqnce should be 15 metre.
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